of Draccena on the other, is i)erfect, and may be 

 followed out in minute detail. 



The evidence in support of the hypothesis 

 that scalariform pitting is primitive is con- 

 vincing. It is evident that the process of the 

 breaking up of scalariform pits into circular 

 pits was in progress in the antecedent cycads, 

 and that this process started first in the tra- 

 cheid side-walls, whereby the overlapping tra- 

 cheid ends became more conservative than 

 their truly lateral portions. The complement- 

 ary relations in the wood of the cycadeoids 

 and cycads outlined in Wieland's recent note^ 

 are thus anatomically reconciled. The origin 

 of branched bars is also explained. 



Excellent examples to show that perfect 

 scalariform tracheids exist in living types 

 occur in Magnolia hypoleuca. The scalari- 

 form pitting very closely approximates that 

 of Cytadeoidea Dartoni. Scalariform tra- 

 cheids slightly more advanced may be found 

 in the aquifoliaceous Byronia sandwicensis 

 Endl. Here the tracheids retain typical sca- 

 lariform bordered pits at the overlapping ends, 

 with the exception that occasional shorter pits 

 are present and in a position to form branched 

 bars should the pit membranes and pit borders 

 be eliminated. The lateral walls show perfect 

 transition from scalariform to circular pits. 

 Living types, therefore, preserve all stages in 

 the transformation of scalariform tracheids 

 into vessels with multiseriate circular pits 

 and simple perforations; and there is every 

 reason to believe that modification is still go- 

 ing on. 



Many seem to be under the impression that 

 scalariform pitting is of rare occurrence above 

 the cycads. A close comparison of scalariform 

 tracheids, which Wieland's material makes pos- 

 sible, can leave no doubt that existing forms, 

 in dicotyledons as well as in monocotyledons, 



iWieland, G. R., Feb., 1918, "Cycadoid Wood 

 Structure," Science, N. S., XLVII., pp. 141, 142. 



